This invention relates to a fuel injector for use in delivering fuel under pressure to a combustion space of an internal combustion engine. The invention relates, in particular, to a fuel injector suitable for use in a common rail fuel system for delivering fuel to a compression ignition internal combustion engine, the injector being of the type in which the distance through which the injector needle moves during an injection cycle is controlled.
It is known to use two- or multi-stage lift fuel injectors to permit the rate at which fuel is delivered or the fuel spray pattern to be varied, in use. This may be achieved, for example, by locating an inner needle within a bore formed in an outer needle, the inner needle being arranged to remain seated when the outer needle is moved by a small distance, moving away from its seating when the outer needle is moved by a larger distance. In such an arrangement, injection of fuel may occur, for example, through a few outlet openings upon the initial small movement of the outer needle and through a greater number of openings following the subsequent movement of the outer and inner needles. As a result, the injection rate and spray pattern may be varied, in use. Other injection parameters may also be controlled or varied using this technique. It will be appreciated, however, that other techniques for controlling the various injection parameters by controlling the distance moved by a valve needle are known.
The distance through which the valve needle is moved is typically controlled by controlling the energization level, and hence axial length, of a piezoelectric stack. Such an actuation technique is thought to be undesirable as piezoelectric stacks of dimensions suitable for use in such applications are relatively expensive and are difficult to control. It is an object of the invention to provide a fuel injector in which the distance moved by a valve needle thereof can be controlled and in which the disadvantages mentioned hereinbefore are obviated or mitigated.
According to the present invention there is provided a fuel injector comprising a valve needle slidable within a bore, a surface associated with the needle being exposed to the fuel pressure within a first control chamber, movement of the needle away from a seating being limited by a moveable stop member, the stop member having a surface exposed to the fuel pressure within a second control chamber, and a valve arrangement controlling the fuel pressures within the first and second control chamber to control the positions of the needle and the moveable stop member.
By appropriately controlling the fuel pressures applied to the first and second control chambers, the valve needle can be held in either a closed position, an intermediate position or a fully lifted position. Depending upon the nature of the valve needle and any additional needle, sleeve or adjustment member associated with the valve needle, such control of the position of the valve needle may be used to control the fuel injection rate, spray pattern or other injection parameters.
The valve arrangement conveniently includes a common actuator arranged to control operation of a first valve associated with the first control chamber and a second valve associated with the second control chamber. The actuator may, for example, comprise an electromagnetic actuator or a piezoelectric stack. It will be appreciated, however, that the first and second valves may be controlled by respective actuators. Conveniently, the fuel injector includes a control valve arrangement including a valve member having first and second seating surfaces. The first seating surface may be defined by a seating member located within a further chamber. The further chamber may be defined, at least in part, by a bore within which the valve member is slidable. The second seating surface may be defined by a region of the bore.
The control valve arrangement may be arranged such that fuel pressure within the first and second control chambers can be controlled by varying the rate of movement of the valve member away from the first seating surface.
Preferably, the control valve arrangement may be arranged such that, in use, movement of the valve member at a relatively high rate causes movement of the valve needle away from the valve needle seating into a first fuel injecting position to permit fuel delivery through a first outlet opening.
Preferably, the control valve arrangement may be arranged such that movement of the valve member at a relatively low rate causes movement of the valve needle away from the valve needle seating into a second fuel injecting position to permit fuel delivery through the first outlet opening and a second outlet opening.
Alternatively, or in addition, the control valve arrangement may be arranged such that movement of the valve member back and forth between the first and second seating surfaces causes movement of the valve needle into the second fuel injecting position.
Alternatively, or in addition, the control valve arrangement may be arranged such that movement of the valve member into an intermediate position away from both the first and second seating surfaces permits movement of the valve needle into the second fuel injecting position.
The control valve arrangement may be arranged to permit the rate of valve needle movement away from the valve needle seating to be varied, in use.
The fuel injector may be of the inwardly opening type.
The valve needle may take the form of an outer valve needle which is engageable with a seating to control fuel delivery through a first outlet opening, the fuel injector including an inner valve needle which is slidable within an additional bore provided in the outer valve needle and is engageable with a further seating to control fuel delivery through a second outlet opening. The inner valve needle and the outer valve needle may be arranged such that movement of the outer valve needle beyond a predetermined amount transmits movement to the inner valve needle to move the inner valve needle away from the further seating. Alternatively, the valve needle may be of the outwardly opening type, in which case the valve needle may be provided with first and second axially spaced outlet passages and whereby, in use, movement of the valve needle outwardly within the first bore by a first amount causes fuel to be delivered through only the first outlet passage and movement of the valve needle outwardly within the first bore by a further amount causes fuel to be delivered through both the first and second outlet passages.
The movement of the valve member may be controlled, in use, by means of an electromagnetic actuator arrangement or by means of a piezoelectric actuator arrangement.
According to a second aspect of the present invention, there is provided a fuel injector comprising a valve needle slidable within a first bore and engageable with a valve needle seating to control fuel delivery through an outlet opening, a surface associated with the valve needle being exposed to the fuel pressure within a control chamber, and a control valve arrangement for controlling the fuel pressure within the control chamber to control movement of the valve needle, the control valve arrangement being arranged to permit the rate of valve needle movement away from the valve needle seating to be varied, in use.
As the rate of valve needle movement can be varied, in use, the rate of increase of fuel delivery can be varied.
Preferably, the control chamber may have, associated therewith, first and second passage means for permitting fuel to escape from the control chamber.
Conveniently, the control valve arrangement may be arranged to operate in either a first mode of operation, in which the rate of valve needle movement away from the valve needle seating is governed by the dimensions of the first passage means, or a second mode of operation, in which the rate of valve needle movement away from the valve needle seating is governed by the dimensions of the second passage means.
The valve needle in accordance with this embodiment of the invention may be of the inwardly or outwardly opening type.
It will be appreciated that the fuel injector of the present invention may include a plurality of first and second outlet openings.
According to a further aspect of the invention, there is provided a fuel injector arrangement comprising a plurality of fuel injectors as described herein, a first rail for delivering pressurised fuel to the injectors, a second rail communicating with the second control chamber of each of the injectors and a valve arrangement for controlling communication between the second rail and a low pressure fuel reservoir.